This invention relates to plastic injection molded fans positioned in a shroud to blow air through a downstream heat exchanger.
Important considerations in the design of a fan shroud include maximum efficiency, minimum noise, and economy of manufacture. Specifically, fan shrouds are designed to: provide smooth flow of air into the entire fan disk area; minimize the flow of air that recirculates from the fan outlet to the inlet through the running clearances between the fan and shroud; and to permit one piece injection molding of parts.
It is common for cooling fans (particularly fans for automotive applications) to be configured in a shroud to blow air through a downstream heat exchanger. It may be advantageous in applications of such fans to use a banded fan, i.e., one in which the blade tips are connected by a rotating ring. Such a construction avoids generating a blade tip vortex such as would be generated by unbanded fan blades, thus reducing noise and increasing efficiency. Such a construction also enhances blade strength, thus permitting added fan blade skew to further reduce noise. See, e.g., Gray U.S. Pat. No. 4,358,245; Gray U.S. Pat. No. 4,548,548; Gray U.S. Pat. No. 4,569,631, each of which is hereby incorporated by reference.
It is desirable in certain applications to support the fan drive system on the upstream side of the fan.
It also may be desirable to cover the fan inlet with a guard to prevent injury from accidental contact with the rotating fan blades, however such constructions can interfere with desirable smooth airflow.
Specific prior art constructions are disclosed in the following documents.
Anderson U.S. Pat. Nos. 2,225,406, Gerlitz 3,433,403; and Bede 4,657,483 disclose shroud inlets for unbanded fans. The shroud surface adjacent to the fan is a smooth continuation of the inlet surface.
Funk U.S. Pat. Nos. 2,303,832 and Scoates 4,927,328 disclose unbanded fans running in shrouds that provide both axial and radial running clearances. The inlet diameter of the shrouds are substantially smaller than that of the fan blades.
Soulez-Lariviere, U.S. Pat. No. 3,620,640 discloses an unbanded fan operating in a shroud having a continuous surface forming the fan inlet and fan outlet.
Hayashi U.S. Pat. No. 4,396,351 discloses a banded fan and shroud combination in which the shroud terminates adjacent the fan in a straight (unflared) section having a diameter greater than the fan blade diameter.
Longhouse U. S. Pat. Nos. 4,213,426 and 4,329,946 disclose banded engine cooling fans in which the inlet flaring is formed as part of the rotating band.
Hauser U.S. Pat. No. 4,566,852 discloses a banded engine cooling fan with a shroud having an inlet diameter substantially smaller than that of the fan blades, and having an inlet lip that encloses the inlet end of the fan band.